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bpo-37612: always call linkat() from os.link(), if available#14843

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jo-he wants to merge 2 commits into
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bpo-37612: always call linkat() from os.link(), if available#14843
jo-he wants to merge 2 commits into
python:mainfrom
jo-he:master

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@jo-he

@jo-he jo-he commented Jul 18, 2019 •
edited by bedevere-bot
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The issue with link() is, that POSIX does not define its behavior regarding symbolic links:

"If path1 names a symbolic link, it is implementation-defined whether link() follows the symbolic link, or creates a new link to the symbolic link itself."

And it is indeed implemented differently on e.g. Linux and NetBSD. So, it makes no sense to call link(), where linkat() is available.

https://bugs.python.org/issue37612

@jo-he
bpo-37612: always call linkat() from os.link(), if available …
ae2e6e8 
The issue with link() is that POSIX does not define its behavior
regarding symbolic links:

"If path1 names a symbolic link, it is implementation-defined whether
link() follows the symbolic link, or creates a new link to the symbolic
link itself."

And it is indeed implemented differently on Linux and NetBSD.
@gnprice

gnprice commented Aug 1, 2019

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As I understand it from your bpo report, the issue is that the behavior of os.link doesn't match its documentation on some platforms (in particular Linux), and this fixes things so that it does.

In particular the actual behavior on such platforms makes follow_symlinks=True useless, even when explicitly specified, so that's definitely a bug. (Also you located the relevant provision in POSIX and found that Linux's behavior here is perfectly compliant.)

That sounds like a good fix to me!

Would you add a test for it? See test_os.py, or perhaps test_posix.py if the test doesn't make sense to run on Windows.

@takluyver takluyver mentioned this pull request Mar 23, 2021
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@takluyver

takluyver commented Mar 23, 2021

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I've had a go at adding the test in #24997.

@bedevere-app bedevere-app Bot mentioned this pull request Apr 14, 2025
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@python-cla-bot

python-cla-bot Bot commented Apr 18, 2025

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The following commit authors need to sign the Contributor License Agreement:

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@serhiy-storchaka

serhiy-storchaka commented May 4, 2025

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Fixed by #132517.

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@jo-he @gnprice @takluyver @serhiy-storchaka @the-knights-who-say-ni @ezio-melotti @bedevere-bot